Designs of flexible structures such as buildings, aircraft, radar installations, solar panels and the like are generally efficient and cost effective with regard to regular periodic loading. This is, in large measure, a result of the fact that this type of loading occurs during a substantial percentage of the lifetime of the structure. Hence, the design is often "on line" to counter these stresses. Although "regular" loading will vary according to the particular structure and its method of use, well-known methods of structural analysis (often computer-aided) achieve high levels of efficiency in the maintenance of deflections within tolerable bounds.
Unfortunately, structural designs must anticipate a certain amount of non-periodic or transient loading. Earthquakes, wind gusts and the like subject structures to deterministic as well as non-stationary random excitations. Efficient, cost-effective design in light of such real-life situations poses difficult problems. Commonly, a large degree of redundancy is incorporated into structures to counteract such forces. Redundancy, by its utilization of substantial additional materials, directly adds to the cost of the structure and, in the case of airborne designs, can substantially increase operating costs.
Some attempts have been made to avoid overdesign for redundancy by "active" as opposed to "passive" methods of vibration control. In this class is included devices such as vibration or mass dampers. Such devices, discussed by S. F. Masri and L. Yang in "Earthquake Response Spectra of Systems Provided with Non-Linear Auxiliary Mass Dampers," (Paper No. 372, Proceedings 5WCEE, Roome (1973)), may be designed for both linear and nonlinear damping. They rely, to a large extent, on the principles of momentum transfer and energy dissipation.
A major drawback of mass dampers is that the forces they exert upon a vibrating structure do not always occur at the proper point in time for optimum reduction of motion and system stress. Thus, an "effective" mass damper may allow an undesirable amount of stress to occur before its effect is realized.
The present invention overcomes the drawbacks of the prior art by providing methods and apparatus for minimizing the stress encountered by a flexible structure when subjected to a shock. The method generally includes sensing the state of the structure in response to the shock. The value of at least one corrective (i.e., motion-attenuating) pulse is then calculated or transmitted in response to the state. Once calculated, a corrective pulse is then applied to the structure to achieve the desired result.
A system is provided by the present invention for practicing the aforesaid method. The system includes a sensor to detect the state of the structure, means responsive to its state to produce a control signal and at least one pulse generator responsive to the signal. Additionally included within the scope of the invention is a building including a flexible main frame engaged to the aforesaid system.
The above and additional features will become apparent from the following detailed description wherein like numerals represent like parts throughout.